Good question. I've wondered the same about one of my Z3 that continues to have tracking problems even after a trip to the factory. As I recall, Swarovski recommends the lightest scope ring tightening of any scope I've played with.
I was a bit disappointed with the tracking of my last Z3 3-9x36. Lovely little scope, but it took longer to sight in than any Leupold I've ever tried (about 20). Ditto for my one and only Meopta.
